JP2003253494A - Method of coating automobile body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of coating an automobile body by which an excellent finish appearance and a coating performance are attained. <P>SOLUTION: In the outer plate part and/or the inner plate member of the automobile body constituted of an oxide film treated aluminum material or a different kind of a metallic material obtained by combining the oxide film treated aluminum material with a steel material as an essential material, the surface roughness of the aluminum material on which an oxide film treatment is to be applied is ≤0.2 μm and the aluminum material treated with an oxide film treatment is coated with a thermal setting type electrodeposition coating film. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method for an automobile body, which is partially or wholly composed of an oxide film-treated aluminum material, in a coating film finish appearance such as image clarity and smoothness, and corrosion resistance. The present invention relates to a coating method for an automobile body which provides a coating film having excellent coating film performance such as processability.

[0002]

2. Description of the Related Art Conventionally, as a method of painting an automobile body, generally, a car body made of steel is subjected to a chemical conversion treatment, and then a primer coating or a top coating is performed. In recent years, in the field of automobiles, the weight of vehicle bodies has become heavier due to the improvement of collision safety performance and the increase of standard equipments, etc., but on the other hand, the substantial improvement in fuel efficiency is required due to the global environmental problems. As one method for satisfying such requirements, it is considered to reduce the weight of the entire automobile by replacing a part or the whole of the automobile body mainly made of steel with an aluminum material. However, there has been a problem that a coating film excellent in the finished appearance and coating film performance cannot be obtained even if the vehicle body part mainly made of aluminum material is coated by a conventional coating method.

[0003]

Means for Solving the Problems As a result of earnest research, the present inventors have found that a coating film coated by a specific coating process can achieve the above-mentioned object, and have completed the present invention. It was

Thus, according to the present invention, 1. An outer plate portion and / or an inner plate of an automobile body whose main material is an oxide film-treated aluminum material or a dissimilar metal material in which an oxide film-treated aluminum material and a steel material are combined. In the department
A method for coating an automobile body, characterized in that the oxide film-treated aluminum material is coated with a thermosetting electrodeposition coating film, 2. In the oxide film-treated aluminum material, the oxide film treatment is a chemical film treatment. 4. The method for coating an automobile body according to 1 above, 3. The method for coating an automobile body according to claim 1, wherein the oxide film treatment is an anodic oxide film treatment in the oxide film-treated aluminum material. 1 or 2 above, wherein the thermosetting electrodeposition coating film is formed of a cationic thermosetting electrodeposition coating composition
5. The method for coating an automobile body according to item 5, wherein the thermosetting electrodeposition coating film is formed of an anion thermosetting electrodeposition paint.
6. The method for coating an automobile body according to claim 6, 6. In the above oxide film-treated aluminum material, the surface roughness of the oxide film-treated aluminum material is Ra of 0.2 μm or less. 7. The method for coating an automobile body according to any one of 1. above, wherein, in the oxide film-treated aluminum material, the oxide film-treated aluminum material is JIS K-6000 series aluminum alloy containing magnesium and silica. 7. The method for coating an automobile body according to any one of 1 to 3 and 6 above, 8. The oxide film-treated aluminum material is colored with a natural coloring film or an electrolytic coloring film. The method for coating an automobile body according to any one of 1 to 3, 6, and 7 above is provided.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The method for coating an automobile body of the present invention is such that a thermosetting electrodeposition coating film is formed on an automobile body which is partially or wholly made of an oxide film-treated aluminum material, and particularly The feature is that a specific aluminum material is used as the oxide film-treated aluminum material.

In the coating method of the present invention, when an oxide film-treated aluminum material is used as a material for an automobile body, for example, (1) a member (engine hood, fender panel, etc.) intended for the metal material is pressed. (2) A coating method in which an electrodeposition coating is carried out after processing, then surface treatment of an oxide film, then mounting the surface-treated member on an automobile body and assembling, and (2) aiming at the metal material. It can be carried out by a coating method in which the member to be pressed is subjected to press processing, surface treatment with an oxidation film, and then electrodeposition coating is performed, and the obtained electrodeposition coated member is attached to an automobile body and assembled.

When a different metal material in which an oxide film-treated aluminum material and a steel material are combined is used as a material for an automobile body, for example, (1) a member intended for an oxide film-treated aluminum material (engine hood, (Fender panel, etc.), then oxide film surface treatment is performed, and the resulting oxide film-treated aluminum member and steel material are pressed into the target member (engine hood, fender panel, etc.), and then surface treatment And then the surface-treated steel member is attached to an automobile body and assembled, and then electrodeposition coating is applied. (2) A member intended for an oxide film-treated aluminum material (engine hood) , Fender panels, etc.), and then subjected to an oxide film surface treatment, and the resulting oxide film-treated aluminum member was electrodeposited Material and an electro-deposited steel material obtained by pressing a target material (engine hood, fender panel, etc.) into steel, then surface-treating, and then electro-depositing the surface-treated steel. It can be done by a painting method in which it is attached to and assembled.

On the surface of the electrodeposition coating film, if necessary, conventionally known chipping primer (barrier coating film, etc.) used in the field of automobile coating, intermediate coating cured coating,
A topcoat cured coating can be formed.

The oxide film-treated aluminum material used in the present invention includes a conventionally known aluminum material which has been subjected to a chemical film treatment or an anodic oxide film treatment.

The aluminum material can be used without particular limitation as long as it has been conventionally considered for automobile bodies. Specifically, JIS A5000 series aluminum alloy plate containing magnesium as an aluminum alloy base material and JI containing magnesium and silica.
Examples include S A6000 series aluminum alloy base materials.

In the present invention, in particular, among these aluminum alloy base materials, the JIS A6000 series aluminum alloy base material has a strength due to the above-mentioned contained metal when the paint is baked a plurality of times at a temperature of 140 ° C. or higher. It is preferable to use the latter one because it imparts hardness. The content of the above metal is preferably in the range of 0.5 to 3%.

Further, in the above-mentioned aluminum material, the surface roughness of the aluminum material (which can be measured using a JIS B06013 three-dimensional roughness meter) is 0.2 μm or less in Ra, particularly 0.1.
It is preferable to use one having a thickness of less than μm. Ra is 0.
If it exceeds 2 μm, the smoothness of the electrodeposition coating film coated on the oxide film-treated aluminum material is reduced, and as a result, the smoothness of the top coating film (such as a feeling of dustiness) is deteriorated, resulting in poor gloss of the coating film. There is a drawback that On the other hand, if Ra is too small, the adhesion between the cationic electrodeposition coating film and the oxide film-treated aluminum material decreases, so it is not preferable to set it to less than 0.01 μm. The surface roughness of such an aluminum material can be adjusted by changing the roughness of the roll at the time of rolling, or by a surface treatment technique such as mechanical polishing, chemical polishing, and electrolytic polishing. As the above-mentioned polishing, electropolishing is particularly preferable because it can facilitate polishing with fine roughness.

Further, as the oxide film treatment of aluminum material,
A conventionally known surface treatment can be performed.

As the chemical film treatment, for example, (1) to
The processing can be performed according to the order of (3).

(1) Pretreatment step: Aluminum material-Mechanical polishing-Degreasing (acid, acid salt, alkali, alkali salt, organic solvent, surfactant, electrolytic degreasing, etc.)-Washing (including neutralization) -Chemical polishing -Washing (2) Chemical film treatment: Phosphate treatment agent (zinc phosphate, iron phosphate, manganese phosphate, etc. to which Albond method belongs), phosphate alcohol treatment agent, chromic acid phosphate treatment agent, Sodium carbonate treatment agent, chromate treatment agent (chromic acid, dichromate, etc.), boehmite method (12
Steam treatment at 0 to 150 ° C, distilled water treatment at 100 ° C, 10
Treatment with distilled water containing amine at 0 ° C.), titanium-based surface treatment agents, fluorine-based surface treatment agents and the like.

Among the above treatments, treatment with a zinc phosphate treating agent is preferable. The treatment is a treatment agent using a compound such as phosphoric acid, zinc acid phosphate, potassium fluoride, etc. as a raw material, and the aluminum is etched by bringing this treatment agent into contact with the anodized film-treated aluminum material. The eluted aluminum reacts with phosphoric acid and hydrofluoric acid to form an aluminum salt, and acidic zinc phosphate (zinc dihydrogen phosphate) reacts with aluminum and hydrofluoric acid to form zinc triphosphate, which is anodized aluminum. It deposits on the material surface and forms a film.

(3) Post-treatment: Washing-drying Further, for the coloring of the chemical film treatment, for example, a method of coloring with the treatment liquid used in the above-mentioned chemical film treatment, a metal salt or the like is further added to the treatment liquid. Examples thereof include a method of coloring, a method of coloring with a complex compound such as potassium permanganate, cobalt, copper, potassium ferrocyanide, iron, and an alizarin colorant.

The above chemical film-treated aluminum material can be subjected to cation electrodeposition coating and anion electrodeposition coating. However, cation electrodeposition coating is particularly preferable because the oxide film treated aluminum material has excellent durability and finished appearance. Is preferably performed.

The anodic oxidation treatment can be carried out, for example, by the following method.

Degreasing-alkali etching-desmut-anodizing treatment-sealing treatment Degreasing-alkali etching-desmut-anodizing treatment-secondary electrolytic coloring Degreasing-polishing (electrolytic polishing, chemical polishing, matte finishing, etc.)-Anodic oxidation Treatment- (Dyeing if necessary) Washing with water was omitted in each step.

As the above-mentioned anodizing treatment, for example,
The sulfuric acid method, oxalic acid method, chromic acid method, boric acid method and the like can be mentioned. Among these, the sulfuric acid method is preferable because it can form a film that is hard and has excellent corrosion resistance. Further, in the process of the above step, the finished appearance of the coating film is excellent, so that the process is preferable.

The above-mentioned anodized film is preferably subjected to anion electrodeposition coating because the durability of the oxide film-treated aluminum material and the finished appearance are excellent.

The anodized film can be colored by natural coloring or electrolytic coloring, if necessary. A colored anodized aluminum material having a film formed thereon can be used. The film formed by spontaneous coloring and electrolytic coloring can be formed by a conventionally known coloring technique. In addition, the method of forming a film by electrolytic coloring, after performing anodization,
This is a method of coloring by performing secondary electrolysis in an electrolytic solution containing a metal salt, or by adding a metal salt to the electrolytic solution for anodic oxidation and coloring it at the same time as the anodizing treatment. Examples of the metal salt include nickel salt, copper salt, tin salt, cobalt salt, lead salt, manganese salt, gold salt, silver salt, molybdenum salt, and selenium salt. Examples of the salt form include inorganic acid salts such as sulfuric acid, organic acid salts such as acetic acid, and oxyacid salts.

In addition to the above-mentioned surface treatment agents, for example, etching agents (inorganic acids, organic acids or salts thereof), heavy metals (Zr, Mo, W, Ti, Mn, Z).
n, Ni, etc.) or a salt thereof (nitric acid, phosphoric acid, hydrofluoric acid, etc.) and, if necessary, a binder (phenol resin, carboxylated polyolefin resin, etc.), a rust inhibitor (vanadic acid, organic phosphonic acid, gallic acid) Acid compounds,
Sulfides, triazine thiols, benzotriazoles, thiocarbonyl compounds, etc.), adhesion promoters (silane coupling agents, silica gel, EROSIL, etc.), which are weakly basic or weakly acid-based organic and / or inorganic substances Surface treatment agents can also be used.

As the above cationic electrodeposition coating, a known cationic electrodeposition coating prepared by mixing and dispersing a cationic resin composition in water can be used. As the cationic resin composition, for example, a composition containing a base resin having a hydroxyl group and a cationic group and a crosslinking agent such as a block polyisocyanate compound is preferably used. As the base resin,
For example, a reaction product of an epoxy resin and a cationizing agent,
A polycondensate of a polycarboxylic acid and a polyamine (see US Pat. No. 2,450,940), which is protonated with an acid, a polyisocyanate compound, and a polyaddition product of a polyol and a mono- or polyamine with an acid. What you did
Acrylic or vinyl-based copolymer containing hydroxyl and amino groups, which is protonated with an acid (Japanese Patent Publication No. 45).
No. -12395, Japanese Patent Publication No. 45-12396), a product obtained by protonating an adduct of a polycarboxylic acid resin and an alkyleneimine (US Pat. No. 340308).
No. 8 specification) and the like.

A coating can be obtained by neutralizing the above-mentioned cationic resin with an acidic neutralizing agent (acetic acid, hydroxyacetic acid, etc.) and dispersing it in water.

Examples of the anion electrodeposition coating material include acrylic resin anion electrodeposition coating material and polyester resin anion electrodeposition coating material.

The above-mentioned acrylic resin anion electrodeposition coating composition is prepared, for example, by adding a curing agent (block polyisocyanate, melamine resin, urea resin, etc.) to a hydroxyl group- and carboxyl group-containing acrylic resin, and by using a basic compound (amine, etc.).
It can be used after being neutralized with and dispersed in water.

The acrylic resin can be obtained by a radical copolymerization reaction of a hydroxyl group-containing (meth) acrylic monomer, α, β-ethylenically unsaturated carboxylic acid and, if necessary, other radical copolymerizable monomer. The radical copolymerization reaction can be carried out by a conventionally known method, for example, a solution polymerization method. Examples of the α, β-ethylenically unsaturated carboxylic acid include (meth) acrylic acid and maleic acid. Further, the hydroxyl group-containing (meth) acrylic monomer and the other radical copolymerizable monomer include the same ones as described above.

The acrylic resin usually has a hydroxyl value of 10 to 3
Within the range of 00 mgKOH / g, preferably 20-200
mgKOH / g, acid value in the range of 20 to 200 mgKOH / g, preferably 30 to 100 mgKOH / g, number average molecular weight in the range of 2,000 to 100,000, preferably 3,000 to 50,000. The inside is appropriate.

The component ratio of the base resin and the curing agent is usually 30 to 1 with respect to 100 parts by weight of the base resin component.
The amount is 00 parts by weight, preferably 40 to 80 parts by weight.

Polyester resin Anion electrodeposition coating composition includes a hydroxyl group- and carboxyl group-containing polyester resin and a curing agent (block polyisocyanate or melamine resin,
A urea resin, etc., which has been blended, neutralized with a basic compound (amine, etc.) and dispersed in water can be used.

Examples of the polyester resin include those obtained by reacting a polyhydric alcohol (neopentyl glycol, 1,6-hexanediol, etc.) and a polybasic acid (terephthalic acid, isophthalic acid, trimellitic acid, etc.). Can be mentioned. If necessary, the above-mentioned monohydric alcohol or monobasic acid can be reacted.

The polyester resin usually has a hydroxyl value of 10
To 300 mgKOH / g, preferably 20 to 2
00 mgKOH / g, acid value 20-200 mgKOH / g
Is suitable, and the number average molecular weight is suitably in the range of 500 to 10,000.

The component ratio of the base resin and the curing agent is usually 30 to 1 with respect to 100 parts by weight of the base resin component.
The amount is 00 parts by weight, preferably 40 to 80 parts by weight.

In addition to the above-mentioned components, the above-mentioned respective cationic or anionic electrodeposition paints may contain a surfactant, a surface conditioner, a curing catalyst, an ultraviolet absorber, an ultraviolet stabilizer, a colorant, and other components, if necessary. Additives can be added.

The cationic electrodeposition coating composition has a solid content of about 5
It is adjusted to 40% by weight and pH within the range of 5-9.

The anion electrodeposition coating composition has a solid content of about 5 to 5.
Adjust to 25% by weight and pH within the range of 7-10.

The electrodeposition coating with a cation or anion electrodeposition coating is carried out by using the above-mentioned electrodeposition coating as an electrodeposition bath and a bath temperature of 15 to 3
The electrodeposition coating can be performed by adjusting the temperature to 5 ° C. and energizing between the object to be coated and the electrode under the load voltage of 100 to 400 V.

After the electrodeposition coating, in order to remove the excess electrodeposition coating, the ultrafiltration filtration liquid (UF filtration liquid), RO permeated water, industrial water, pure water, etc. are electrodeposited on the surface of the coated product. It can be washed with water if necessary so that no paint remains.

The electrodeposition coating film is baked at 1 at the surface temperature of the coating material.
10 ° C to 200 ° C, preferably 140 ° C to 180 ° C, the time is 10 minutes to 180 minutes, preferably 20 minutes to
It can be heated and cured for 50 minutes.

On the surface of the electrodeposition coating film, if necessary, conventionally known chipping primer (barrier coating film, etc.) used in the field of automobile coating, intermediate coating cured coating,
A topcoat cured coating can be formed.

[0043]

EFFECTS OF THE INVENTION Since the present invention has the above-mentioned constitution, it is possible to form an electrodeposition coating film suitable for coating an automobile body easily, economically, labor-saving, safe, stable and continuously. In addition, it is possible to form an electrodeposition coating film having excellent finish appearance and coating film performance. Further, by using an oxide film-treated aluminum material having a surface roughness Ra of 0.2 μm or less, the finished appearance of the electrodeposition coating film can be further improved.

[0044]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. Hereinafter, "parts" and "%" mean "parts by weight" and "% by weight", respectively. The present invention is not limited to the examples below.

Example 1 An aluminum material having a thickness of 0.8 mm (JIS A6061, R
a 0.2 μm) was subjected to a degreasing treatment, an etching treatment, and a smut removal treatment by a conventional method, and then anodized in a 170 g / liter sulfuric acid aqueous solution to form an anodized film having a thickness of 10 μm. Then, after performing a sealing treatment with deionized water at 80 ° C. or higher, the following anion electrodeposition paint is electrodeposited and baked at 170 ° C. for 20 minutes to give a dry film thickness of about 20 μm.
m electrodeposition coated plate was obtained.

Example 2 The aluminum material of the anodized film obtained in Example 1 was subjected to AC secondary electrolysis (15 V, 15 V, in an aqueous solution of 25 g / liter of nickel sulfate).
20 ° C., 2 minutes to 10 minutes) to obtain a bronze colored aluminum material. Then, after sealing treatment with deionized water at 80 ° C. or higher, the following anion electrodeposition paint was electrodeposited to
It was baked at 70 ° C. for 20 minutes to obtain an electrodeposition coated plate having a dry film thickness of about 20 μm.

Example 3 Aluminum material having a plate thickness of 0.8 mm (JIS A6061, R
a 0.2 μm) was subjected to degreasing treatment and boehmite treatment (steam treatment at 120 to 150 ° C.) by an ordinary method to form an oxide film. Next, the following anion electrodeposition paint is electrodeposited and baked at 170 ° C. for 20 minutes to give a dry film thickness of about 20 μm.
The electrodeposition coated board of was obtained.

Example 4 Aluminum material having a plate thickness of 0.8 mm (JIS A6061, R
a 0.2 μm) was subjected to degreasing treatment and boehmite treatment (steam treatment at 120 to 150 ° C.) by an ordinary method to form an oxide film. Then, the following cationic electrodeposition coating is electrodeposition coated and baked at 170 ° C. for 20 minutes to give a dry film thickness of about 20 μm.
The electrodeposition coated board of was obtained.

Example 5 An aluminum material having a plate thickness of 0.8 mm (JIS A6061, R
a 0.2 μm) by a conventional method, and a phosphate surface treatment agent (manganese diphosphate / manganese silicofluoride / potassium fluoride / acidic zinc phosphate / phosphoric acid aqueous solution)
It was immersed at 0 ° C. for 2 to 5 minutes to form a zinc phosphate treatment film. Then, the following anion electrodeposition paint is electrodeposited,
It was baked at 0 ° C. for 20 minutes to obtain an electrodeposition coated plate having a dry film thickness of about 20 μm.

Example 6 An aluminum material having a plate thickness of 0.8 mm (JIS A6061, R
a 0.2 μm) by a conventional method, and a phosphate surface treatment agent (manganese biphosphate / manganese silicofluoride / potassium fluoride / acidic zinc phosphate / phosphoric acid aqueous solution)
It was immersed at 0 ° C. for 2 to 5 minutes to form a zinc phosphate treatment film. Then, the following cationic electrodeposition paint is electrodeposited,
It was baked at 0 ° C. for 20 minutes to obtain an electrodeposition coated plate having a dry film thickness of about 20 μm.

Example 7 A 0.8 mm thick aluminum material (JIS A6061, R
a 0.2 μm) was degreased by a conventional method, and a titanium-treated film was formed using the following titanium-based surface treatment agent. Then, the following anion electrodeposition paint was electrodeposited and baked at 170 ° C. for 20 minutes to obtain an electrodeposition coated plate having a dry film thickness of about 20 μm.

Example 8 Aluminum material having a plate thickness of 0.8 mm (JIS A6061, R
a 0.2 μm) was degreased by a conventional method, and a titanium-treated film was formed using the following titanium-based surface treatment agent. Then, the following cationic electrodeposition paint was electrodeposited and baked at 170 ° C. for 20 minutes to obtain an electrodeposition coated plate having a dry film thickness of about 20 μm.

Comparative Example 1 A zinc-iron alloyed hot-dip galvanized steel sheet surface-treated with a zinc phosphate treating agent was electrodeposited with the following anion electrodeposition coating composition and baked at 170 ° C. for 20 minutes to give a dry film thickness of about 20 μm
The electrodeposition coated board of was obtained.

Comparative Example 2 A zinc-iron alloyed hot-dip galvanized steel sheet surface-treated with a zinc phosphate treating agent was electrodeposited with the following cationic electrodeposition paint, baked at 170 ° C. for 20 minutes, and dried to a film thickness of about 20 μm
The electrodeposition coated board of was obtained.

Cationic electrodeposition paint: Electron GT-10
(Kansai Paint Co., Ltd., block polyisocyanate curing type epoxy resin electrodeposition coating) Anion electrodeposition coating: Electron AG210 (Kansai Paint Co., melamine curing type acrylic resin electrodeposition coating) The results are shown in Table 1.

Table 1

[0057]

[Table 1]

Test method Smoothness of coating surface: The appearance of the coating film after coating was observed with the naked eye, and the appearance of cracked skin, pinholes, unevenness, and appearance was examined. ◯ is good, Δ is a little inferior, and x is inferior.

Adhesion: The coated plate was dipped in warm water at 40 ° C. for 10 days, and then a knife was used to make 11 cuts in each length and width in the width of about 2 mm on the surface of the coating film.
A cellophane adhesive tape having a width of mm was adhered to the adhesive tape, and the adhesiveness of the eye gap portion when strongly peeled off was evaluated according to the following criteria. ◯: No peeling at all, Δ: Slight peeling, ×: Significant peeling.

Corrosion resistance: A cross cut reaching a base material is put in a coated plate, and this is cut according to JIS Z-2371.
After performing a 0-hour salt water spray test, wash with water and evaluate the rust and blister of the general part according to the following criteria, and at the same time, cross-cut part when cellophane adhesive tape is adhered to the cross-cut part and peeled off instantly. The maximum peeling width (one side) of was described. ◯: No rust or blistering on the coated surface, Δ:
Occurrence of slight rust or blisters on the coated surface,
X: Significant rust or blistering was observed on the coated surface.

Salt-water resistance: A cross-cut reaching the substrate is put on a coated plate, immersed in 5% saline for 10 days at 50 ° C., and then washed with water, and rust and blister in the general part are evaluated according to the following criteria. At the same time, the maximum peeling width (one side) of the cross cut portion when the cellophane adhesive tape was adhered to the cross cut portion and peeled off instantly was shown. ◯: No rust or blistering on the coated surface, Δ:
Occurrence of slight rust or blisters on the coated surface,
X: Significant rust or blistering was observed on the coated surface.

Chipping resistance: At -20 ° C, 100 g of crushed stone No. 7 was sprayed onto the coated surface at a pressure of 3 kg / cm ² from an angle of 90 ° to the coated surface, and then the stone-applied surface was covered with gum tape. The peeling test was performed and evaluated according to the following criteria. ◯: No peeling of coating film, Δ: slight peeling of coating film, ×: significant peeling of coating film.

Claims (8)

[Claims] 1. An oxide film treatment in an outer plate portion and / or an inner plate portion of an automobile body, the main material of which is an oxide film-treated aluminum material or a dissimilar metal material in which an oxide film-treated aluminum material and a steel material are combined. A method for coating an automobile body, wherein an aluminum material is coated with a thermosetting electrodeposition coating film. 2. The coating method for an automobile body according to claim 1, wherein in the oxide film-treated aluminum material, the oxide film treatment is a chemical film treatment. 3. The coating method for an automobile body according to claim 1, wherein in the oxide film-treated aluminum material, the oxide film treatment is an anodic oxide film treatment. 4. The method for coating an automobile body according to claim 1, wherein the thermosetting electrodeposition coating film is formed of a cationic thermosetting electrodeposition coating material. 5. The method for coating an automobile body according to claim 1 or 3, wherein the thermosetting electrodeposition coating film is formed of an anion thermosetting electrodeposition coating material. 6. The above-mentioned oxide film-treated aluminum material, wherein the surface roughness of the aluminum material subjected to the oxide film treatment is Ra of 0.
The coating method for an automobile body according to any one of claims 1 to 3, wherein the coating method has a thickness of 2 µm or less. 7. The aluminum material treated with an oxide film in the oxide film-treated aluminum material is a JIS K-6000 series aluminum alloy containing magnesium and silica. One of
The method for coating an automobile body according to paragraph. 8. The automobile body according to claim 1, wherein the oxide film-treated aluminum material is colored with a natural coloring film or an electrolytic coloring film. How to paint.